Extrusion blow molding plastic containers involves extruding a tube of monolayer or multilayer plastic material, capturing the tube between opposed mold sections, blowing the tube to the contours of the mold cavity, opening the mold, removing the container, and trimming the end of the container neck finish. This trimming operation can involve removal of a dome or moil from the neck finish, which is a convenience element for the blow molding operation and can be recycled as process regrind. In another type of extrusion blow molding operation, the trimming operation can involve separation of two containers that are molded end-to-end. In either event, the trimming operation can leave an uneven end surface for sealing engagement with a container closure. Furthermore, the end surface of the container neck finish may have mold parting line seams that can deleteriously affect sealing engagement with a container closure. An object of the present invention is to provide an apparatus and method for reforming the neck finish end surface after the trimming operation to prepare the end surface for enhanced sealing engagement with a closure.
The present invention involves a number of aspects, which can be implemented separately from or in combination with each other.
In accordance with a first aspect of the invention, an apparatus for reforming an annular end sealing surface of a molded plastic container includes a head having an annular contact surface and a drive for bringing the annular contact surface into contact with the annular end sealing surface of the container. The head and the container do not rotate relative to each other during this contact reforming operation. Heat is applied through the contact surface while the surfaces are in contact to raise the temperature at the end sealing surface to at least the softening temperature of the plastic material, so that the end sealing surface is softened and reformed by heat and contact with the contact surface. In one embodiment, the head contact surface is porous, and the end sealing surface is heated by heated air directed through the porous contact surface. In another embodiment, a heater heats at least the annular contact surface of the head, and the heat is transferred by contact to the end sealing surface of the container.
An apparatus for reforming a neck finish end surface on a blow molded plastic container in accordance with another aspect of the present invention includes a head having an internal annular channel and an annular porous ring closing an end of the channel. At least one air flow passage is provided in the head for delivering heated air to the annular channel and through the porous ring to a container neck finish end engaged with the porous metal ring. The heated air heats both the porous ring and the neck finish end surface to soften the neck finish end surface. The neck finish end surface is reformed both by heat from the air and the porous ring, and by contact with the porous ring. In other words, the container neck finish end surface is heated to softening both by conduction from the porous ring and by contact of the heated air, and is reformed by contact with the ring.